As disclosed in Patent Document 1 (below-noted) as well as a large number of references, a copper foil for a conventional printed wiring board is undergone a roughening treatment for forming irregularity by adhering fine copper particles or the like on one surface thereof. When laminating with a base-material resin, such as prepreg, the irregular shape of the roughened copper foil is buried in the base-material resin to obtain an anchor effect, and the adhesiveness of the copper foil to the base-material resin has been obtained.
To take the case of an electrolytic copper foil as an example, the conventional electrolytic copper foil for a printed wiring board is manufactured through an electrolysis step and a surface-treatment step. A bulk copper layer, which is the base material of the electrolytic copper foil, is obtained by flowing a copper electrolyte between a drum-shaped rotating cathode and a lead-based anode disposed facing along the shape of the rotating cathode; depositing copper on the drum surface of the rotating cathode utilizing an electrolytic reaction to be a state of a copper foil; and continuously peeling the foil off the rotating cathode. The copper foil in this stage is herein referred to as an untreated foil.
Since the shape of the mirror-finished surface of the rotating cathode is transferred to the surface of the untreated foil that has contacted the rotating cathode, and the surface is shinny and flat, it is referred to as a shinny surface. Whereas, since the crystal growth rate of the deposited copper is different for each crystal face, the surface shape of the solution side, which is the depositing side, shows a mountain-shaped irregularity, and it is referred to as a rough surface. Normally, the rough surface becomes the surface for laminating with the insulation material when a copper-clad laminate is manufactured.
Next, the untreated foil is undergone the roughening treatment and anticorrosive treatment to the rough surface by the surface-treatment step. The roughening treatment to the rough surface prevents the dropout of fine copper particles by supplying the current of so-called burn-plating conditions in a copper sulfate solution to deposit fine copper particles on the mountain-shaped irregularity of the rough surface, and immediately performing cover plating in the current range of the flat-plating conditions. Therefore, the rough surface after depositing fine copper particles is referred to as a “roughening-treated surface”. Then, an anticorrosive treatment or the like is performed as required, to complete an electrolytic copper foil.
In recent years, however, following the trend of miniaturization and sophistication of electronic devices incorporating printed wiring boards, requirements for the wiring density of printed wiring boards are increasing every year. Moreover, the improvement as the product quality has been demanded, there have been the high degree of requirements circuit shapes themselves formed by etching, and circuit etching factors of the level wherein impedance control can be perfectly performed have been demanded.
Therefore, in order to solve the problems of the etching factors of such a circuit, as disclosed in Patent Document 2 (below-noted), there have been attempts to obtain good laminating adhesiveness without the roughening treatment by providing two resin layers having different compositions for securing adhesion to the base-material resin on the surface of a copper foil without the roughening treatment.
Patent Document 1: Japanese Patent Laid-Open No. 05-029740
Patent Document 2: Japanese Patent Laid-Open No. 11-10794